The present invention relates to polyethylene glycol modified copolyester fibers that have exceptional moisture management characteristics and that can be formed into exceptionally comfortable fabrics.
Polyester filament is strong, yet lightweight, and has excellent elastic memory characteristics. Polyester fabric resists wrinkles and creases, retains its shape in garments, resists abrasions, dries quickly, and requires minimal care. Because it is synthetic, however, polyester is often considered to have an unacceptable appearance for garment purposes when initially formed as a filament. Accordingly, polyester filaments require texturing to produce acceptable characteristics of appearance, hand, and comfort in yarns and fabrics. Even then, polyester is often viewed unfavorably in garments.
In pursuit of improved polyesters, various chemical modifications have been attempted to obtain desirable textile features. Unfortunately, some such treatments can produce unexpected or unwanted characteristics in the modified polyester. For example, polyethylene glycol enhances certain polyester properties, such as dye uptake, but diminishes other properties-especially those melt phase characteristics that are critical to filament spinning. Consequently, manufacturers have found that significant fractions of polyethylene glycol in copolyester can complicatexe2x80x94and even precludexe2x80x94the commercial production of acceptable copolyester filaments. To gain commercial acceptance, modified polyesters must be compatible with commercial equipment with respect to melt-spinning, texturing, yarn spinning, fabric forming (e.g., weaving and knitting), and fabric finishing. This need for processing compatibility through conventional equipment has constrained the development of innovative polyester compositions.
To overcome the limitations of polyester compositions, polyester fibers are often blended with other kinds of fibers, both synthetic and natural. Perhaps most widely used in clothing are blended yarns and fabrics made of polyester and cotton. In general, blended fabrics of polyester and cotton are formed by spinning blended yarn from cotton fibers and polyester staple fibers. The blended yarns can then be woven or knitted into fabrics.
Cotton, like polyester, has certain advantages and disadvantages. Cotton is formed almost entirely of pure cellulose. Cotton fibers are typically about one inch long, but can vary from about one half inch to more than two inches. Mature cotton fibers are characterized by their convolutions. Under a microscope, cotton appears as a twisted ribbon with thickened edges. Cotton is lightweight, absorbs moisture quickly and easily, and has a generally favorable texture (i.e., hand) when woven into fabrics. Cotton, however, lacks strength characteristics and elastic memory. Consequently, garments formed entirely of cotton require frequent laundering and pressing.
Blends of cotton and polyester fibers have found wide-ranging acceptance as they combine the desirable characteristics of each. Even so, there are continuing efforts to develop polyester filament, yarns, and fabrics that more closely resemble those of cotton, silk, rayon, or other natural fibers. One example is polyester microfibers, which are characterized by extremely fine filaments that offer exceptionally good aesthetics and hand, while retaining the benefits of polyester. Polyester microfibers, however, have proved to be difficult to dye because of their high degree of molecular orientation and crystallinity.
A need continues to exist, however, for enhanced polyester compositions that have properties similar to those of cotton and other natural fibers, while retaining the advantages of polyester. Research and development by Wellman, Inc. demonstrates that improved wicking may be achieved in copolyester fibers, yarns, and fabrics by selectively incorporating polyethylene glycol.
For example, one such PEG-modified composition and method for producing the same is disclosed by Nichols et al. in commonly-assigned, pending U.S. patent application Ser. No. 09/141,665, filed Aug. 28, 1998, for Polyester Modified with Polyethylene Glycol and Pentaerythritol. U.S. patent application Ser. No. 09/141,665, which is incorporated entirely herein by reference, discloses a polyester composition that includes polyethylene terephthalate, polyethylene glycol in an amount sufficient to increase the wetting and wicking properties of a fiber made from the composition to a level substantially similar to the properties of cotton, but less than the amount that would reduce the favorable elastic memory properties of the polyester composition, and chain branching agent in an amount that raises the melt viscosity of the polyester composition to a level that permits filament manufacture under substantially normal spinning conditions. Including significant concentrations of branching agents to increase melt viscosity is sometimes undesirable, however, because branching agents promote cross-linking. This reduces filament strength, which can lead to processing failures.
Another method for achieving enhanced polyester fibers is described by Branum in commonly-assigned, pending U.S. patent application Ser. No. 09/444,192, filed Nov. 19, 1999, for a Method of Preparing Polyethylene Glycol Modified Polyester Filaments. U.S. patent application Ser. No. 09/444,192, which, as noted, is incorporated entirely herein by reference, describes copolymerizing polyethylene glycol, which typically makes up between about 4 percent and 20 percent by weight of the resulting copolyester, into polyethylene terephthalate in the melt-phase to a-relatively low intrinsic viscosity (i.e., a viscosity that will not support filament spinning). The resulting PEG-modified polyester is then further polymerized in the solid phase until the copolyester is capable of achieving a melt viscosity sufficient to spin filaments. By introducing a solid state polymerization (SSP) step, this method reduces the need to add branching agents, such as pentaerythritol, to increase the melt-phase polymerization rate and thereby achieve an intrinsic viscosity that facilitates the spinning of filaments. U.S. patent application Ser. No. 09/444,192 explains that branching agents promote cross-linking, which can lead to relatively weaker textiles.
Furthermore, a related method for achieving enhanced polyester fibers is described by Branum in commonly-assigned, pending application Ser. No. 09/484,822, filed Jan. 18, 2000, for Polyethylene Glycol Modified Polyester Fibers and Method for Making the Same. U.S. patent application Ser. No. 09/484,822, which is a continuation-in-part of the aforementioned application Ser. No. 09/444,192 and which is also incorporated entirely herein by reference, describes copolymerizing polyethylene glycol and branching agent into polyethylene terephthalate in the melt-phase to form a copolyester composition having an intrinsic viscosity of at least about 0.67 dl/g. Thereafter, copolyester filaments can be spun from the copolyester composition.
The foregoing PEG-modified copolyester fibers may be advantageously incorporated into products as discussed by Branum et al. in pending application Ser. No. 09/761,446, filed Jan. 17, 2001, for Nonwoven Fabrics Formed from Polyethylene Glycol Modified Polyester Fibers and Method for Making the Same. U.S. patent application Ser. No. 09/761,446, which is a continuation-in-part of the aforementioned application Ser. No. 09/484,822 and which is also incorporated entirely herein by reference, describes a nonwoven fabric that is formed of polyethylene glycol modified copolyester fibers that include polyethylene terephthalate in an amount sufficient for the copolyester staple fibers to possess dimensional stability properties (e.g., shrinkage during home laundering) substantially similar to those of conventional, unmodified polyethylene terephthalate fibers, polyethylene glycol in an amount sufficient for the copolyester fibers to possess wicking characteristics that are superior to those of conventional, unmodified polyethylene terephthalate fibers, and chain branching agent in an amount less than about 0.0014 mole-equivalent branches per mole of standardized polymer.
Furthermore, related PEG-modified copolyester compositions, fibers, yarns, and fabrics are described by Nichols et al. in commonly-assigned, pending application Ser. No. 09/801,583, filed Mar. 8, 2001, for Polyethylene Glycol Modified Polyester Fibers and Method for Making the Same. U.S. patent application Ser. No. 09/801,583, which is a continuation-in-part of the aforementioned, commonly-assigned applications, is also incorporated entirely herein by reference.
As discussed in U.S. patent application Ser. No. 09/761,446 for Nonwoven Fabrics Formed from Polyethylene Glycol Modified Polyester Fibers and Method for Making the Same, the improved wicking that may be achieved in copolyester fibers by selectively incorporating polyethylene glycol is advantageous in nonwoven fabrics. In particular, nonwoven personal care products employing this technology family possess exceptional moisture management characteristics and may be formed at significantly lower calendar bonding temperatures.
In this regard, disposable diapers and other personal care products formed of nonwoven, synthetic fabrics are extremely popular. In fact, disposable diapers made of such nonwoven fabrics have now essentially replaced cloth diapers in the marketplace. This is so not only because nonwoven fabrics offer an attractive cost structure, but also because nonwoven fabrics provide superior performance. For example, continued enhancements to nonwoven fabrics include weight reduction, aesthetic improvements, and, of particular relevance to diapers, increases in the number of uses an article can endure before requiring disposal.
For many years, synthetic fibers, particularly polyester fibers, have been a major component in nonwoven fabrics for disposable personal care products. Such man-made fibers are cost-effective, strong, and are readily modifiable to deliver a range of desirable properties. For example, denier, crimp, cut length, polymer chemistry, and fiber finish chemistry can all be modified to meet specific end-use requirements. In this regard, coarser deniers are used to increase bulk, cut length can be optimized for various web formation techniques, and fiber finishes are modified to offer processing advantages, as well as end-use performance.
As is known by those familiar with personal care products, a primary function of the nonwoven surge layer in diapers is to move moisture from its source to a highly absorbent core. This allows the fabric surface that is in contact with skin to remain essentially dry and be available to accept more moisture. This increases the duration that a product can be used before disposal. Surge layers are often chemically treated to facilitate this kind of moisture movement. Such treatments, however, are typically inadequate to permit multiple uses, which the marketplace demands for diapers. Consequently, the optimization of the specific diaper construction, including the incorporation of specific fibers and fabrics, is a major focus of research across the fiber, nonwovens, and personal products industries.
The use of nonwoven materials in personal care products is well known. In this regard, U.S. Pat. Nos. 5,879,343, 5,820,973, and 5,994,615, each of which is assigned to Kimberly-Clark Worldwide, Inc., disclose achieving favorable moisture transport properties in surge layers using synthetic fibers, as well as surge materials for disposable personal care products made by bonding fibrous webs. Similarly, U.S. Pat. No. 4,548,856, which is also assigned to Kimberly-Clark Worldwide, Inc., discloses a method for forming bulky, absorbent nonwoven fabrics that include thermoplastic fibers. These Kimberly-Clark patents are hereby incorporated entirely herein by reference.
Despite the advancements in technology, there remains a continuing need for yarns and fabrics having improved moisture management properties.
Therefore, it is an object of this invention to provide a polyethylene glycol modified copolyester fiber that has exceptional moisture management characteristics and that can be formed into exceptionally comfortable fabrics.
It is another object of this invention to provide a polyethylene glycol modified copolyester composition that is particularly suitable for such fibers.
It is yet another object of the present invention to provide methods of preparing polyethylene glycol modified copolyester fibers that can be formed into exceptionally comfortable fabrics.
In this regard, it is a further object of the invention to provide a polyethylene glycol modified copolyester fiber that, while possessing wicking, drying, flame-retardancy, abrasion-resistance, soft hand, dye uptake, and static-dissipation properties that are superior to those of conventional polyethylene terephthalate fibers, can nonetheless be processed using conventional melt spinning equipment.
Finally, it is an object of this invention to provide a nonwoven fabric having exceptional moisture management characteristics. The nonwoven fabric is especially useful in absorbent, personal care products, such as wipes, absorbent undergarments (e.g., disposable diapers, training pants, and adult incontinence products), feminine hygiene products (e.g., sanitary napkins), and even durable goods that have the appearance, performance, and aesthetics of conventional textile goods.
The foregoing, as well as other objectives and advantages of the invention and the manner in which the same are accomplished, is further specified within the following detailed description and its accompanying drawings.